This section provides background information related to the present disclosure which is not necessarily prior art.
The consumers of modern automotive vehicles are increasingly influenced in their purchasing decisions and in their opinions of the quality of a vehicle by their satisfaction with the vehicle's sound quality. In this regard, consumers increasingly expect the interior of the vehicle to be quiet and free of noise from the power train and drive line. Consequently, vehicle manufacturers and their suppliers are under constant pressure to reduce noise to meet the increasingly stringent expectations of consumers.
Drive line components and their integration into a vehicle typically play a significant role in sound quality of a vehicle as they can provide the forcing function that excites specific driveline, suspension and body resonances to produce noise. Since this noise can be tonal in nature, it is usually readily detected by the occupants of a vehicle regardless of other noise levels. Common driveline excitation sources can include driveline imbalance and/or run-out, fluctuations in engine torque, engine idle shake, and motion variation in the meshing gear teeth of the hypoid gear set (i.e., the pinion gear and the ring gear of a differential assembly).
Motion variation is the slight variation in angular displacement between the input and output gears of a gear set. This variation is typically very small and can be on the order of tens of millionths of an inch (measured tangentially at the pitch line of the gear) for a modern automotive differential assembly. Motion variation is typically not constant (e.g., it will typically vary as a function of load, temperature, gearset build position, and break-in wear) and moreover, it cannot be reduced beyond certain levels without severe economic penalties.
Propeller (prop) shafts are typically employed to transmit rotary power in a drive line. Modern automotive propshafts are commonly formed of relatively thin-walled steel or aluminum tubing and as such, can be receptive to various driveline excitation sources. The various excitation sources can typically cause the propshaft to vibrate in a bending (lateral) mode, a torsion mode and a shell mode. Bending mode vibration is a phenomenon wherein energy is transmitted longitudinally along the shaft and causes the shaft to bend at one or more locations. Torsion mode vibration is a phenomenon wherein energy is transmitted tangentially through the shaft and causes the shaft to twist. Shell mode vibration is a phenomenon wherein a standing wave is transmitted circumferentially about the shaft and causes the cross-section of the shaft to deflect or bend along one or more axes.
Several techniques have been employed to attenuate vibrations in propshafts including the use of weights and liners. U.S. Pat. No. 2,001,166 to Swennes, for example, discloses the use of a pair of discrete plugs or weights to attenuate vibrations. The weights of the '166 patent are frictionally engaged to the propshaft at experimentally-derived locations and as such, it appears that the weights are employed as a resistive means to attenuate bending mode vibration. As used herein, resistive attenuation of vibration refers to a vibration attenuation means that deforms as vibration energy is transmitted through it (i.e., the vibration attenuation means) so that the vibration attenuation means absorbs (and thereby attenuates) the vibration energy. While this technique can be effective, the additional mass of the weights can require changes in the propshaft mounting hardware and/or propshaft geometry (e.g., wall thickness) and/or can change the critical speed of the propshaft. Moreover, as the plugs tend to be relatively short, they typically would not effectively attenuate shell mode vibration or torsion mode vibration.
U.S. Pat. No. 3,075,406 to Butler Jr., et al. appears to disclose a single damper that is inserted to a hollow shaft. The damper includes a pair of resilient members, which frictionally engage the interior surface of the hollow shaft, and a metal bar that is suspended within the interior of the hollow shaft by the resilient members. The '406 patent explains that at the resonant vibration frequency of the propeller shaft, “the motion of the mass is out of phase with the radial motion of the tubular propeller shaft”. Accordingly, the damper of the '406 patent appears to be a reactive damper for attenuating bending mode vibration. As used herein, reactive attenuation of vibration refers to a mechanism that can oscillate in opposition to the vibration energy to thereby “cancel out” a portion of the vibration energy. The damper of the '406 patent appears to be ineffective at attenuating torsion mode vibration and shell mode vibration due to its relatively short length and its contact with a relatively small portion of the interior surface of the propshaft.
U.S. Pat. No. 2,751,765 to Rowland et al., U.S. Pat. No. 4,014,184 to Stark and U.S. Pat. Nos. 4,909,361 and 5,976,021 to Stark et al. disclose hollow liners for a propshaft. The '765 and '184 patents appear to disclose hollow multi-ply cardboard liners that are press-fit to the propshaft; the cardboard liners are relatively long and appear to extend substantially coextensively with the hollow shaft. The '361 and '021 patents appear to disclose liners having a hollow cardboard core and a helical retaining strip that extends a relatively short distance (e.g., 0.03 inch) from the outside diameter of the core. The retaining strip has high frictional properties to frictionally engage the propshaft. Accordingly, the liners of the '765, '184, '361 and '021 patents appear to disclose a resistive means for attenuating shell mode vibration. These liners, however, do not appear to be suitable for attenuating bending mode vibration or torsion mode vibration.
In view of the foregoing, there remains a need in the art for an improved method for damping various types of vibrations in a hollow shaft. This method facilitates the damping of shell mode vibration as well as the damping of bending mode vibration and/or torsion mode vibration.